Kawase blur effect
This is a faster version of the traditional "Blur" effect. It's recommended that you use this one rather than the "Gaussian" blur effect.
The Blur property sets the overall strength of the blur, while Quality controls how smooth it looks (higher values are smoother but more costly to render).
The Pixelize X and Pixelize Y properties let you blur more on one axis than the other. Setting different values for each creates a directional blur — for example, a strong horizontal blur to suggest fast sideways movement.
Reference
All effects are listed in the effects reference page.